 When you hold in mind a sentence you have just read or a phone number you’re about to dial, you’re engaging a critical brain system known as working memory.
For the past several decades, neuroscientists have believed that as information is held in working memory, brain cells associated with that information fire continuously. However, a new study from MIT has upended that theory, instead finding that as information is held in working memory, neurons fire in sporadic, coordinated bursts. These cyclical bursts could help the brain to hold multiple items in working memory at the same time, according to the researchers. “By having these different bursts coming at different moments in time, you can keep different items in memory separate from one another,” says Earl Miller, the Picower Professor in MIT’s Picower Institute for Learning and Memory and the Department of Brain and Cognitive Sciences. According to the new model, information is stored in rapid changes in the synaptic strength of the neurons. The brief bursts serve to “imprint” information in the synapses of these neurons, and the bursts reoccur periodically to reinforce the information as long as it is needed. Mikael Lundqvist, a Picower Institute postdoc, and Jonas Rose, now at University of Tubingen in Germany, are the paper’s lead authors. The bursts create waves of coordinated activity in the gamma frequency (45 to 100 hertz), like the ones that were observed in the data. These waves occur sporadically, with gaps between them, and each ensemble of neurons, encoding a specific item, produces a different burst of gamma waves. “It’s like a fingerprint,” Lundqvist says.
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